The bunny ears in this emoji actually originated from the 'Bunny Girl' outfits worn by waitresses at the American 'Playboy Club' in the 1960s. However, it's now mostly used without any connection to that historical meaning.

Because they are wearing matching outfits and doing the same dance, it's used not just for partying but also to emphasize perfect sync or teamwork. It's ideal for expressing a situation where two people are perfectly in tune, like the synchronized dancing of an idol group.